EP0174479A2 - Polyvinyl butyral with a reduced adhesion and increased tensile strength - Google Patents

Abstract

Polyvinylbutyral with reduced stickiness and improved tear strength, produced by acetalization of association-capable polyvinyl alcohol in the associated state with n-butyraldehyde in the aqueous phase in the presence of an acidic catalyst. %. the acetalization preferably starting at temperatures below 20 ° C. and the temperature being raised to above 40 ° C. in the course of the reaction. Use for the production of plasticized thermoplastic polyvinyl butyral films and their use as a composite layer in glass composites

Description

The invention relates to polyvinyl butyral with reduced stickiness and improved tear strength, process for its production and its use for the production of thermoplastic molding compositions containing plasticizer, in particular high-strength films, which are outstandingly suitable as a connecting intermediate layer in the production of laminated glass.

It is known that polyvinyl butyral can be processed with the addition of plasticizer to give films which can be used as an intermediate layer in laminated glass. One of the methods for producing suitable polyvinyl butyral is e.g. in the reaction of an aqueous polyvinyl alcohol solution with n-butyraldehyde in the presence of a strong acid.

EP-PS 0000699 describes a process in which an aftertreatment phase at 50 to 70 ° C. follows the usual production method for polyvinyl butyral in the presence of an emulsifying organic sulfonic acid. From such a post-treated polyvinyl butyral, films can be produced with the addition of a plasticizer, which have a higher strength, a higher viscosity and a reduced tack.

In the aftermath there has been no lack of attempts to achieve the advantageous properties of these polyvinyl butyral polymers aftertreated in the manner described above. One of the reasons for the search for an improved process was the technically controllable, but corrosive effect of the sulfonic acid component.

For example, it has been proposed to emulsify the organic sulfonic acid or its salts with water-soluble salts of perchloric acid, hydrochloric acid, hydrobromic acid, and nitric acid to replace acid or thiocyanic acid. However, these salts are much less effective than the organic sulfonates mentioned. They must therefore be used in a considerably higher concentration, which leads to difficulties in working up the polymers, the corrosion problems in their production are aggravated and, moreover, is less economical.

All processes have in common that the aftertreatment leads to an increase in the intermolecular forces between the polymer molecules.

The increase in hydrogen bonds can be recognized, for example, by a broadening of the OH band in the infrared spectrum.

From the disadvantages in the production of improved polyvinyl butyrals which have become known from the prior art, it follows that there is undiminished a considerable need to achieve an increase in the intermolecular forces in polyvinyl butyral by simpler methods.

It has now surprisingly been found that, while overcoming the known difficulties and disadvantages, polyvinyl butyral with considerably improved properties can be obtained by acetalizing associative polyvinyl alcohol in the associated state in the aqueous phase.

The invention therefore relates to a process for the preparation of polyvinyl butyral with reduced stickiness and improved tear strength by acetalizing polyvinyl alcohol with n-butyraldehyde in the aqueous phase in the presence of an acidic catalyst, characterized in that associative polyvinyl alcohol is acetalized in the associated state.

According to the invention, any polyvinyl alcohols can be used as starting components which can form associates in aqueous solution. A preferred embodiment of the invention consists in that the association ability of polyvinyl alcohol can be increased accordingly by reducing its content of acetyl groups.

The production process according to the invention is distinguished from known polyvinyl butyral production processes, among others. characterized in that it can be carried out under milder reaction conditions, e.g. shorter reaction times, lower temperatures and / or lower concentrations of emulsifying organic sulfonic acid, or also the complete absence of such sulfonic acids or additions of salts. Compared to polyvinyl butyral, which was produced from unassociated polyvinyl alcohol, polyvinyl butyral produced according to the invention has higher intermolecular forces. Plasticized films made from the polymer produced according to the invention flow less well at temperatures below 100 ° C., are stronger and less sticky than plasticized polyvinyl butyrals produced comparatively from unassociated polyvinyl alcohol.

Also surprising is the excellent optical clarity of plasticized polyvinyl butyral films produced according to the invention. In contrast, it is pointed out in the literature that in the preparation of polyvinyl butyral in the aqueous phase, an association of the polyvinyl alcohol, which can occur, for example, when the acetalization temperature is too low, must be avoided, since the resulting polyvinyl butyral would otherwise no longer be clear in conventional solvents, to which plasticizers can also be counted (cf. Piastro et al. Soviet Plastics 1970, No. 2, page 7). In contrast to this finding, known from the literature, results in the processing of fiction according to the polyvinyl butyrals produced, with the usual plasticizers, clear films.

In the production of polyvinyl butyral according to the invention it is important that the polyvinyl alcohol to be reacted is present in an aqueous solution in an associated form before the reaction with n-butyraldehyde begins. As already mentioned, any polyvinyl alcohols can be used as starting components, provided that they can form associates in aqueous solution. Another condition is that the aqueous solutions of the associated polyvinyl alcohol are still flowable under acetalization conditions. Whether an associate to be used according to the invention is present can easily be recognized from the fact that the aqueous polyvinyl alcohol solution, after heating to a temperature of 90 to 100 ° C. and cooling to room temperature, shows an increase in viscosity upon standing.

In the case of polyvinyl alcohols with contents of less than 1% by weight, preferably less than 0.5% by weight, of vinyl acetate units, an association - recognizable by the increase in viscosity of the solution when left to stand at a low temperature - can be achieved relatively easily by, for example, the Store solution at low temperature for several days before acetalization. The association is accelerated by cooling to low temperatures down to -5 ° C. It is also advantageous to associate a commercially available polyvinyl alcohol which contains more than 1% by weight and preferably less than 5% by weight of vinyl acetate units and which is not or only slightly associated at room temperature in aqueous solution by means of complete or partial saponification thereof accelerate any acetyl groups still present. The resulting saponified polyvinyl alcohol should contain less than 1% by weight, preferably less than 0.5% by weight, of residual vinyl acetate units. The saponification can easily be carried out by adding stoichiometric amounts of alkali, for example aqueous sodium hydroxide solution or potassium hydroxide solution to the aqueous solution of the polyvinyl alcohol, preferably with stirring at elevated temperatures between 30 and 100 ° C., preferably 50 to 95 ° C. (see, for example, DE-OS 2039467). Depending on the final residual acetyl content, the polyvinyl alcohol can be associated in a short or very short time. In the case of practically 100% saponified polyvinyl alcohol, an association can have taken place at low temperature, for example after 5 to 10 minutes. It is usually not necessary to store the solution for longer than 24 hours. The temperature at which the association occurs is preferably below 40 ° C., in particular between 15 and 20 ° C. The association time is preferably at least 10 minutes and can be up to 24 hours. In some cases it may also be sufficient if only a part of the polyvinyl alcohol, preferably at least 20% by weight of the total amount, is saponified in the manner mentioned above.

The associated polyvinyl alcohol is then reacted with n-butyraldehyde in the aqueous phase by known methods.

Another object of the invention is therefore a process for the preparation of polyvinyl butyral with reduced stickiness and improved tear strength by acetalization of polyvinyl alcohol with n-butyraldehyde in the aqueous phase in the presence of an acidic catalyst, characterized in that polyvinyl alcohol with more than 1 wt .-% , preferably 1 to 5% by weight of vinyl acetate units in aqueous solution with addition of alkali to a content of less than 1% by weight, preferably less than 0.5% by weight, of vinyl acetate units and the saponified polyvinyl alcohol in the aqueous solution acetalized in the associated state.

As already mentioned, the preparation of polyvinyl butyral polymers according to the invention in the aqueous phase can become known methods. The reaction with n-butyraldehyde is carried out in the presence of strong, preferably inorganic acids, such as, for example, hydrochloric acid, sulfuric acid or nitric acid, in a concentration of 0.1 to 5% by weight, based on the aqueous phase. A method is preferred in which the acetalization begins below 20 ° C., preferably at 0 to 15 ° C., and the temperature is increased to above 40 ° C. in the course of the reaction.

If appropriate, in addition to the mineral acid, any emulsifiers can advantageously be present, in particular an emulsifying organic sulfonic acid or its salts. Furthermore, other salts such as alkali chlorides, bromides, nitrates, perchlorates or acetates can also be added. The presence of these additives can be particularly advantageous if the actual preparation of the polymer is followed by an aftertreatment phase of 0.5 to 10 hours, preferably 1 to 7 hours, at 50 ° C. to 70 ° C. The concentration of the additives, depending on their different effectiveness, is preferably between 0.01 and 20% by weight, based on polyvinyl butyral. It is particularly advantageous to use up to 1% by weight, in particular from 0.01 to 0.5% by weight, preferably from 0.05 to 0.4% by weight, of an emulsifying organic sulfonic acid with e.g. 8 to 30 carbon atoms or their salts.

In principle, polyvinyl alcohols with low to high molecular weights are suitable for the production of polyvinyl butyral. For the production of composite films, however, polyvinyl butyrals are required which have a viscosity (measured according to DIN 53015 on a 5% strength by weight solution in ethanol at 23 ° C.) of 10 to 200 mPa · s, preferably 50 to 100 mPa · s , exhibit. This viscosity is adjusted by selecting appropriate polyvinyl alcohols.

The resulting polyvinyl butyral may have a residual content Have vinyl alcohol units of 14 to 28% by weight, preferably 15 to 24% by weight. This vinyl alcohol content can be adjusted by varying the amount of butyraldehyde used in the acetalization.

After the polyvinyl butyral has been separated off from the aqueous phase, the polymer is washed neutral as usual, preferably with a small amount of alkali and dried by known methods. The processing of polyvinyl butyral into plasticized composite films is also carried out according to known methods together with a plasticizer.

The amount of the plasticizer to be added in the manufacture of the composite film is generally 20 to 50 parts by weight per 100 parts by weight of polyvinyl butyral. The commonly used compounds, e.g. Esters of polyhydric alcohols or of polyvalent acids. For example, esters of triethylene glycol with aliphatic carboxylic acids having 6 to 10 carbon atoms, such as in particular 2-ethyl butyric acid, glycerol monooleate, dibutyl sebacate, di (β-butoxymethyl) adipate, dioctyl phthalate and tricresyl phosphate, are suitable. These plasticizers can be used individually or in mixtures.

Substances can also be added which stabilize the mixture against degradation, e.g. Small amounts of alkali or of alkaline salts, furthermore oxidation stabilizers such as the phenols, bisphenols or terpene phenols substituted in the 2-, 4-, and / or 6-position.

Finally, the mixtures can also contain additives which influence the adhesion of the films to one another or to glass, e.g. Salts of carboxylic acids, fluorides, lecithin or alkylene ureas.

Both the stabilizers mentioned and the additives for Influencing the adhesion can usually be added in amounts of 0.001 to 1 percent by weight, based on the total mixture. Polyvinyl butyral, plasticizers and, if appropriate, additives can be mixed in a known manner by stirring together and, if appropriate, leaving the mixture to stand, or by kneading or rolling at elevated temperature or else directly during processing on the calender or in the extruder.

The production of glass composites from composite films which contain polyvinyl butyral produced according to the invention can be carried out by the customary methods, for example by pressing between two glass panes at 120 to 160 ° C. and 5 to 20 bar.

Polyvinyl butyral produced according to the invention from associated polyvinyl alcohol is new per se. Its surprisingly beneficial properties, such as its reduced stickiness, its improved tear resistance and its reduced flowability can, among other things, may be explained by the fact that in the associative polyvinyl alcohol molecules, for. B. blocks of syndiotactic polyvinyl alcohol sequences are present, which can associate with similar sequences of adjacent polyvinyl alcohol molecules with the formation of solid hydrogen bonds. During the acetalization reaction of the polyvinyl alcohol in the associated state in the aqueous phase, the hydrogen bonds between the polyvinyl alcohol sequences mentioned remain surprisingly evident, possibly up to a maximum of 50 to 70 ° C., and bring about permanent partial physical crosslinking in the resulting polyvinyl butyral.

Further objects of the invention are the use of plasticized polyvinyl butyral according to the invention in the form of thermoplastic films for the production of glass composites, and glass composites which the latter film as Composite layer included.

The invention is illustrated by the following examples.

example 1 a) (comparison)

1000 parts by weight of a 10% by weight aqueous polyvinyl alcohol solution (degree of polymerization P _n approx. 1400, vinyl acetate units 2.2% by weight, based on the polymer), which had previously been kept at 15 ° C. for 1 hour, are mixed with 65 parts by weight Concentrated hydrochloric acid mixed and the mixture reacted at 15 ° C with n-butyraldehyde. 58 parts by weight of n-butyraldehyde are added continuously over the course of 30 minutes. The resulting polyvinyl butyral is finely divided. 30 minutes after the end of the aldehyde addition, the reaction mixture is heated to 58 ° C. at a rate of 20 ° C./hour. When this temperature is reached, 0.15 part by weight of C ₁₅ -alkanesulfonic acid is added and the mixture is stirred at 58 ° C. for 5 hours. It is then cooled, the polyvinyl butyral filtered off, washed neutral with water, stirred with a mixture of 750 parts by weight of water and 2.5 parts by weight of 10% strength by weight sodium hydroxide solution at 60 ° C. for 1 hour, filtered and dried at 40 ° C. in vacuo. The powdery polymer is mixed with 29% by weight (based on the mixture) of triethylene glycol bis-2-ethylbutyric acid ester as plasticizer and 0.01% by weight of potassium formate (10% by weight in water) and to a 76 mm thick film extruded. From the at 23 ° C and 50% rel. Air-conditioned film is made with 3 mm thick float glass 30 x 30 cm large glass composites in an autoclave at 12 bar and 140 ° C.

b) (according to the invention)

The polyvinyl alcohol solution used in experiment a) is heated to 90 ° C. before the acetalization, with stirring at 7.5 Parts by weight of 10% strength by weight sodium hydroxide solution are added and the mixture is kept at this temperature for 30 minutes. As a result of this measure, the content of vinyl acetate units in the polyvinyl alcohol drops to 0.6% by weight. After cooling the solution to 15 ° C., the polyvinyl alcohol is reacted with butyraldehyde as described under a), the reaction mixture is worked up, the polymer is processed into a film and the film is processed into a glass composite.

Dus Beispiel macht deutlich, daß eine Verminderung des Acetylgruppengehaltes im Polyvinylalkohol die Assoziation des Polymerisats fördert, und daß sich diese Assoziation auch nach der Acetalisierung durch eine höhere Lösungs-und Schmelzviskosität des Polyvinylbutyrals bemerkbar macht. Darüber hinaus resultiert bei dem erfindungsgemäß hergestellten Polymerisat des Beispiels 1b) eine Verminderung der Klebrigkeit.The polyvinyl butyral polymers obtained according to Example 1a) and b) and the plasticizer-containing films or glass composites produced therefrom have the properties shown in Table 1.

The example makes it clear that a reduction in the acetyl group content in the polyvinyl alcohol promotes the association of the polymer, and that this association is also noticeable after the acetalization by a higher solution and melt viscosity of the polyvinyl butyral. In addition, the polymer of Example 1b) produced according to the invention results in a reduction in the stickiness.

Example 2

In a manner similar to that described in Example 1, a polyvinyl alcohol with a degree of polymerization P of approximately 1300 and a content of vinyl acetate units of 1.8% by weight is acetalized. The polyvinyl alcohol is reacted once in its original state with n-butyraldehyde (example 2a, comparison) and once after the acetyl groups have been completely saponified (example 2b, according to the invention). For this saponification, 1000 parts by weight of 10% by weight polyvinyl alcohol solution with 10 parts by weight of 10% by weight sodium hydroxide solution are stirred at 90 ° C. for 30 minutes. After cooling to room temperature, the saponified polyvinyl alcohol solution is left to stand for 24 hours and then acetalized. The acetalization is carried out as described in Example 1, but with the following changes: absence of alkanesulfonic acid, amount of n-butyraldehyde = 57 parts by weight, heating at a rate of 20 ° C./hour to 60 ° C. and holding at this temperature for 1 hour. The polymers are worked up and films are produced as described in Example 1.

The polyvinyl butyral polymers and the plasticizer-containing films produced therefrom have the properties shown in Table 2.

Example 3

In the same way as described in Example 2, in the case of a polyvinyl alcohol with a degree of polymerization P _n of approximately 1400, the content of vinyl acetate units is reduced by post-saponification from 1.6 to 0.4 wt obtained a vinyl alcohol unit content of 19.8 wt .-%. A 5% by weight solution of this polyvinyl butyral polymer in ethanol prepared at room temperature has a viscosity of 140 mPa.s. at 23 ° C.

Films made from this polyvinyl butyral with a content of 29% by weight of triethylene glycol bis-heptanoic acid ester as plasticizers have a tear strength of 27.5 N / mm ² and a melt index i ₁₀ at 150 ° C. of 2.8 g / 10 min.

• Viskosität: 80 mPa·s,
• Reißfestigkeit: 26 N/mm²,
• Schmelzindex i₁₀ bei 150°C: 4,4 g/10 Min.

A polyvinyl butyral produced in parallel from the untreated, ie not post-saponified, starting polyvinyl alcohol and processed comparatively gives the following values:

• Viscosity: 80 mPas,
• Tensile strength: 26 N / mm ² ,
• Melt index i ₁₀ at 150 ° C: 4.4 g / 10 min.

Example 4 a) (according to the invention)

1000 parts by weight of a 10 wt .-% solution of polyvinyl alcohol with a degree of polymerization P _n of about 1300 and a content of vinyl acetate units of 1.8 wt .-% are heated to 90 ° C and after adding 9.3 parts by weight 10 wt .-% sodium hydroxide solution stirred at 90 ° C for 30 minutes. The solution is then cooled to 16 ° C., the cooling time being between 40 ° C. and 16 ° C. for 20 minutes, and 65 parts by weight of concentrated hydrochloric acid are added. 57.6 parts by weight of n-butyraldehyde are added continuously to this mixture over the course of 20 minutes. One hour after the end of the aldehyde addition, the mixture is heated to 50 ° C. in one hour with stirring and kept at this temperature for three hours. After the workup described in Example 1, a powdery polyvinyl butyral is obtained with a content of 21.6% by weight of vinyl alcohol units and 0.1% by weight of vinyl acetate units. The polymer is with 29 wt .-% triethylene glycol bis-heptanoic acid ester as a plasticizer and 0.015 wt .-% potassium formate (10 wt .-% in water), based on the mixture, mixed and extruded to a 0.76 mm thick film. Glass composites are produced from the film as described in Example 1.

b) (comparison)

Example 4 a) is repeated, with the difference that the polyvinyl alcohol serving as the starting material is acetalized without post-saponification. In addition, in contrast to Example 4a) above, 0.15 parts by weight of sodium dodecylbenzenesulfonate are added to the acetalization mixture. Otherwise, the acetalization conditions do not differ from Example 4a). A polyvinyl butyral with a vinyl alcohol unit content of 21.3% by weight is obtained. Films and glass composites are produced from this polyvinyl butyral, as described in Example 4a).

The polyvinyl butyral polymers obtained according to Example 4 a) and b) and the plasticizer-containing films or glass composites produced therefrom have the properties shown in Table 3.

The glass composites produced according to Example 4 a) and b) are completely clear and transparent.

Claims (11)

1. A process for the preparation of polyvinyl butyral with reduced stickiness and improved tear strength by acetalization of polyvinyl alcohol with n-butyraldehyde in the aqueous phase in the presence of an acid catalyst, characterized in that associative polyvinyl alcohol is acetalized in the associated state. 2. The method according to claim 1, characterized in that the polyvinyl alcohol contains less than 1 wt .-%, vinyl acetate units. 3. The method according to claim 1 and 2, characterized in that polyvinyl alcohol is saponified with more than 1 wt .-% vinyl acetate units in aqueous solution with addition of alkali to a content of less than 1 wt .-% vinyl acetate units and the saponified polyvinyl alcohol in the aqueous Solution acetalized in the associated state. 4. The method according to claims 1 to 3, characterized in that the associative polyvinyl alcohol is brought into the required associated state before the acetalization by keeping its aqueous solution at a low temperature for at least 10 minutes. 5. Process according to Claims 1 to 4, characterized in that the acetalization begins at temperatures below 20'C and the temperature increases to over 40 ° C in the course of the reaction. _b . Process according to Claims 1 to 5, characterized in that the resulting polyvinyl butyral is subjected to an after-treatment under acetalization conditions at 50 to 70 ° C in the presence of up to 1% by weight of an emulsifying organic sulfonic acid having 8 to 30 C atoms or their salts becomes. 7. The method according to claims 1 to 6, characterized in that the resulting polyvinyl butyral has a residual vinyl alcohol unit content of 14 to 28 wt .-%. 8. The method according to claims 1 to 7, characterized in that the resulting polyvinyl butyral has a viscosity (measured according to DIN 53015 on a 5 wt .-% solution in ethanol at 23 ° C) between 10 and 200 mPa · s. 9. polyvinyl butyral, produced according to one of claims 1 to 8. 10. Use of plasticized polyvinyl butyral films containing polyvinyl butyral according to claim 9 for the production of glass composites. 11. Glass composites containing plasticized polyvinyl butyral film according to claim 10 as a composite layer.